Energy Resources: BiogasWhat
is Biogas?
Biogas is naturally produced when any organic matter
decomposes under anaerobic conditions (in the absence of
oxygen).

The gas consists mainly of
methane (CH4) and carbon dioxide (CO2) in approximately 3:2
ratio.

Methane is the
important component, as it is a highly flammable gas that
can be utilized as fuel for cooking, lighting, water heaters
and, if the sulphur is removed, it can be used to run
biogas-fuelled generators to produce electricity.

Biogas can be produced
under controlled circumstances in specially designed biogas
digesters.

There are many types of
digesters that are being used throughout the world. In
countries such as Germany, biogas technology is highly
advanced and applied primarily to produce green electricity
in the megawatt range. In other developing countries such as
India and China, a more basic technology is used to provide
energy primarily for cooking purposes. India for instance,
has more than a million digesters producing all the cooking
energy for thousands of villages using human (sewerage) and
animal (manure) waste in the process. One of the major
spin-offs of using a biogas digester, is that the spent
material is in the form of organic compost that can then be
used to increase the yield of planted crops.

The Benefits of Biogas
The use of biogas is practically limitless.

As a combined sewerage management/biogas producing system,
any new house, guest house, lodge, development, golf estate,
clinic, hotel, etc. can install a biogas digester system. It
can be their primary sewerage system, or a source of
alternative and sustainable energy in the form of biogas.
The digestate can be applied directly as organic compost, or
the water can be recycled through a wetland.

Commercially biogas digester systems can be installed at
dairies, piggeries, chicken farms, abbotoirs or any other
type of industry where waste containing organic material is
produced, to generate green sustainable electricity.

A biogas digester has the following advantages:

It produces methane gas that can be used for cooking
purposes, lighting, water heating and to generate
electricity
It digests organic waste (from the kitchen, garden,
sewerage, animal manure, etc.)
It prevents methane gas from entering the atmosphere
(methane gas is 20 times more harmful to the environment
than CO2)
It produces organic compost as waste product (in liquid,
slurry or solid form)
Who Can Use Biogas?

SMALLHOLDINGS:
The ideal application for the Puxin Family Size Digester
(10m3 digester) is for smallholdings, especially if there is
some access to animal manure. Adding animal manure over and
above the household sewerage, greatly increases the
production of methane gas. Practical use of the gas is
primarily for cooking purposes, but the gas can also be used
in the Puxin biogas water heater, biogas lights and to
generate (standby) electricity by using a biogas generator.

LARGER SETUPS:
The next market segment is for larger setups such as guest
houses, schools, clinics, or small farms where multiple
units of the 10m3 digester are used. Sizing of the system is
directly proportional to the amount of material fed into the
digester, whether the system is designed primarily as a
sewerage system or for the production of biogas. The amount
of methane produced is dependent on the amount of gas
producing material fed into the digester, limited to an
approximate maximum of 5m3 of gas per 10m³ digester per day.

COMMERCIAL FARMING CONCERNS:
Dairies, pig farms and chicken farms that produce large
quantities of manure fall into this category. Implementing a
biogas digester system for these concerns could potentially
be of enormous financial benefit for such ventures. Under
normal circumstances the huge amounts of manure produced is
more of a liability than an asset and either gets dumped or
sold to composting companies for a nominal fee. By
installing a biogas digester system, the manure now becomes
a major asset, able to produce practically free energy. This
energy in the form of biogas can now be utilized to generate
electricity, heat water, provide lighting or could be used
for cooking purposes by the personnel on site.

For this type of application Biogas SA will install their
large 100m3 Puxin digester in conjunction with multiple gas
holders. Biogas SA can supply and commission any size of
biogas generator from a small 5kVA to very large 500kVA
unit, depending on client's requirements.

MUNICIPAL SEWERAGE WORKS:
The Puxin technology is ideally suited to design and
construct major sewerage works. Biogas technology can be
used to replace existing technology and practices at our
municipal sewerage works, not only providing a better way to
deal with raw sewerage, but providing free energy in the
process.

Due to various reasons, a large number of our municipal
sewerage works have become inefficient, is starting to cause
serious pollution problems and is contributing to large
scale contaminations of our precious water resources in
South Africa. Commissioning biogas systems to replace the
failing sewerage works has the potential to change this
potentially disastrous situation into a win-win situation
for all parties concerned.

The cost of such biogas installations could be offset by
claiming international carbon credits, the biogas generated
could be used to generate electricity that could either be
sold back to the grid or be used locally and the spent
slurry could be sold off as organic compost. The major
advantage to the environment is that the eventual effluent
produced, will be of such a standard that it could in actual
fact improve the quality of the water of the rivers it gets
pumped into!

Biogas SA with its association with The Shenzhen Puxin
Science and Technology Company of China, is in a position to
provide the full spectrum from design to implementation of
fully functional, technologically advanced, biogas digester
systems for the management of large scale sewerage works.
This is applicable not only for municipal sewerage works,
but also for any large scale residential developments,
housing estates, golf estate developments, etc.

PUBLIC SECTOR INSTITUTIONS:
Biogas SA can provide a service to all kinds/levels of
public sector institutions such as schools, clinics,
national parks, etc. and can be particularly effective if we
could get involved during the design stage of such projects.
It is a lot more cost effective to incorporate a biogas
digester as part of the initial design, rather than doing a
retro-fit at a later stage.

WASTE RECYCLING PLANTS:
Any form of organic waste can be used as fuel for a biogas
digester to produce methane. This introduces a whole new
market not previously addressed by traditional digesters due
to the difficulty of removing the solid spent waste from the
digester. The Puxin digester has a large fiberglass
reinforced dome that can easily be removed (no danger of
trapped gas), giving easy access to clean the digester out
and re-load with fresh material.

This means that any type of organic waste material generated
such as agricultural waste, restaurant/hotel food waste,
municipal garden waste, waste from fresh produce markets,
abattoir waste and any other waste one can think of as long
as it is organic in nature. It can potentially be a solution
to the water hyacinth problem!

Tapping into free energy in the form of methane gas by
feeding organic waste into a biogas digester is one of the
most practical and cost effective ways to generate
alternative, sustainable and environmentally friendly energy
for all in South Africa.

THE PUXIN DIGESTER:
Biogas SA is the sole licensee for South Africa of the
Shenzhen Puxin Science and Technology Company (Puxin) of
China. Puxin has developed over a period of 20 years a
unique, patented hydraulic biogas digester that has
eliminated all the disadvantages and enhanced the advantages
of the more traditional fixed and floating dome type
digester designs. As acknowledgement of its technology and
contribution to promoting efficient alternative energy
resources, Puxin was awarded the prestigious Global Top Ten
Investment Scenarios to Apply New Technologies for Renewable
Energy Utilization BlueSky Award in 2006, initiated by the
United Nations Industrial Development Organisation.

The Puxin digester basically consists of a belly, a neck,
the plastic gas holder or dome, an inlet and an outlet. One
of the main features of the digester is the fact that it
basically functions as a hydraulic system. The entire
digester is flooded with water, with the water at the same
level in the inlet, digester neck and outlet. The fact the
decomposition of the material now takes place under water,
creates the ideal anaerobic conditions so critical for the
creation of methane gas. The added advantage of the water is
that it is also responsible for creating the constant
pressure under which the biogas is available in this type of
digester.

As the biogas is produced in the bottom of the digester
belly, it rises upwards and is eventually caught in the
dome. As the volume of gas increases, it starts to replace
the water in a downward direction. The resulting upward
pressure of the replaced water ensures that the collected
biogas in the dome is always under constant pressure (up to
8 bar). The fact that the gas is always available at the
same constant pressure is a major advantage for the
efficient running of most gas appliances. It is practically
impossible to run a generator for instance, if the gas
feeding the generator is not available under constant
pressure; the generator will simply cut out every time the
pressure drops.

Another advantage of the Puxin design, is the ease with
which the digester can be emptied out. Because it is so easy
to clean, any type of organic material can be used as feeder
material. Where it is not practical to empty a digester
(fixed dome type), only material such as manure that leaves
now solid residuals after the decomposition process is
complete, can be used as feeder material. Organic waste such
as leaves, straw, grass, etc do not decompose to the same
extent as manure and will always leave solid waste after
decomposition. This spent material needs to be removed from
the digester before the digester can be reloaded with new
material. The light weight Puxin digester dome can easily be
removed by two people, making it a practical system suitable
to use organic waste as feeder material. This is a major
advantage for applications where manure is not available in
the necessary quantities, but enough organic material is
available.